TS 250 Oil Leak

[parrbd]

Can you feel any play in the mains? Can you feel any roughness when rotating the crankshaft? Are there any burrs or dings on the crankshaft that could be damaging the seal lip? When you have the crank seals and the oil guide plate out you should be able to inspect the bearings, you may need a torch. If no sign of roughness on the inner and outer tracks and balls then bearings should be OK.

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[Kruh]

I actually took off the cylinder in the mean time, since the exhaust was off already and it pretty easy to take the cylinder off.
Piston looks great all around
The bore is also good.

There is nothing unusual in the crankcafe that I can see. Maybe too oily in my opinion.

Since its off, I can feel the bearings without resistance from the piston.
And I can't feel any play. The crank spins very smoothly without any resistance

No, there are no burrs or dings. There were rust spots, but they came off pretty easy. And now its smooth.

Wish i checked the bearing the last time i took it off. Now I don't have a replacement seal.

But I think the bearings are fine.

I'm running out of ideas.


But Iv been thinking abot the whole oil guide plate thing.
How does the oil guide plate work? I mean, premix gets in thru the feed hole and then what? The clearance of that plate between the crank and block are pretty thight and there is no drain hole. Doesn't the area between the seal and oil guide plate get filled up with oil and the pressure, that the piston creates as its coming down, pushes that oil out of the seal? In that scenario there probably isn't a lot of air in that gap to compress. And if the left seal also leaks, the additional oild doesn't help...

I've never seen a plate like that between the seal and bearing on any other bike. The mixture can freely go thru the bearing to the seal and back on other engines.

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[Kruh]

But the oil feed also goes to the seal area. It goes between the oil guide plate and seal.
And I see no way the oil could drain out. Since the clearance between the shaft is pretty tight. So it can drain only slowly thru the gap. But while its running, I imagine it pools up in there.

[Kruh]

Took the seal and plate off

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[Kruh]

Yes the older ES engines as well as 1st generation TS are like you've said.
But mine is a TS250/1. Its the newer, 5 speed model and the engine is basically the same as the ETZ engines.

So the bearing and seal get lubricated by the fuel.

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[Blurredman]

There was a case on this forum where someone had built up an etz250 engine, but did not include the little rubber seal between the two crankcases. They found that transmission oil was being lost and burnt.

This video shows it at 37:39: "seperating rubber plug"
https://www.youtube.com/watch?v=e71KJeBD76Y


If it is on the TS 250/1 as well, do you know whether you included it? I don't know why it would give issues of transmission oil coming out of the seal, unless it was due to pressure build up in combustion (?)

[Kruh]

Yes, I definitely installed that rubber plug.

2 more comments:
- Most of the hole is at the bearing side
- What's all that black stuff on the bearing cages? Castrol synthetic does not do that.

Not really, the oil guide plate blocks it so most of it is on the seal side.
Also, since the plate is right up against the outer bearing race i kinda seals the bearing off from that oil feed.

Now, I'm not a 100% sure how its suppose to work. And I checked many times if everything is installed correctly. But (in my case atleast) it seems to me like that oil guide plate works as a barrier since the clearance between the crank and bearing is pretty tight. Which doesn't allow fuel to exit (at least whilw the engine is running). And so, the fuel/oil pools up between the plate and seal. Which is kind of the intent, so that the seal gets lubricated. But I think it gets filled up too much and the pressure makes it leak.

And as I took the seal off (right after a ride), a bunch of fuel came out too.

Anyways, to test that theory, I drilled a hole in the plate to allow it to easily drain.
Its positioned at a level of about middle of the shaft. The idea of it is to maintain a level of oil so that the crank is partially soaked and can lubricate the seal.

With that modification, I installed an old seal (since I didn't have any new seal on hand).
And after a ride, there isn't a single drop of oil. Even though I used an old seal...
Seems like that fixed it.





Is there something to this? Not sure...
But pretty much every other 2 stroke has a seal right next to the bearing. No plates or anything.
Even the ETZ 125/150 engines have no plates and the same oil feed style.
So it would probably be just fine even without those plates...


Now, despite all that, I don't see other people having problems with any of this.
So why do I have the seal issue, no idea.
But I checked all of your guys suggestions, and everything checks out. I can't find any other cause...

So I'll replace both seals and probably do the mod to the other side as well.



Now, the black stuff on the bearings... No clue what that could be
Maybe burnt oil or something?

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[Kruh]

Of course, MZ had great engineers. They probably had a very good reason to make it that way. And if that design worked for such a long time, the issue is certantly something else. It might be related to the design, but caused by something...
Although, that doesn't mean there arent still some shortcomings. And this plate hole is the only thing that gave me positive results.

In fact, since the last post, I left the bearing as is (with the black stuff) and installed the plate (with the hole) and old seal. As I said, no leaks.

Since then I took apart the engine. The interesting thing was that the bearing was now almost completle clean of that black stuff. Which means the fuel coming from the feed to the plate-seal area now goes directly to the bearing and cleaning it. More importatnly, that means plenty of fuel goes to the bearing which only helps lubrication. So I would come to the conclusion that this does work.


Anyways, I checked everything inside the engine.
-The seal between the cases was good; sealant is all over the mating surfaces.
-As far as the crankshaft balance goes. I took it to a shop to measure the play. And the crank is perfect.
-Contacting surface on the crank is also good on both sides
-Bearings are fine, a bit more play than I'd like. But nothing excessive.
-The rubber plug was in place.
-The left side (clutch side) seal looks good.
-Oil in the gearbox was a good gold color. Amount of oil drained was a bit above 850 ml (some of it stayed in the engine and spilled out while dissasembly). So it doesn't seem that it was leaking gearbox oil into the crankcase
-As we already concluded, the piston does not indicate blowby
-All the plates, seals, clips, bearings were installed just as in the video and books


What is left?
I'm completly clueless.

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[Kruh]

It sure did.
Here's the picture of that bearing I'm talking about (after the modification). It is quite a difference comapred to the picture in the previous post.

Btw, it is not 'play' that is the issue, but 'runout', measured with measurements clocks as shown in all manuals.

Yes, that's what I meant. Didn't express myself properly.

Also the piston...





The black stuff on the clutch side aswell.

They are high-speed bearings with more play, also when new.

I know, but they still have more play than new. They have more play than the old original ones. And the original ones are suoppose to be C4 (though it doesn't say that on the actual bearing). While the new ones I put in were C3

As I was shopping for new bearings, I realized that the last time, I bought sealed bearings.
Of course, I opened them up, but didn't clean the grease they had preapplied. So the goopy black stuff is could be that grease. I find it odd that it would stick around after 4000 km, but who knows...
Regardless of where it came from, my takeaway is that it shows a lack of fuel circulation which would keep things clean and lubricated.



As far as the smoke goes. Most likely a carb related issue.
I use the same oil in my other bike, which doesn't smoke at all (visually). But I will certantly try another oil.
Also, I don't actually know how much smoke is too much. Don't have too much experience with big 2 strokes. So it might not be so bad. I know that 125 and 250 dirt bikes smoke quite a lot more than my MZ.